,2 CTENOPHORA. 



The pharynx (PL III. Fig. i, PI. VIII, Figs. 12— 14, PI. VII, Fig. 3, o. e.) has the walls rather 

 strongly folded, except in the uppermost part, the folds protruding into its lumen. It is very probable 

 that only the upper, smooth part corresponds to the pharynx of the grown animal, in which there are 

 likewise no folds (PI. VII, Fig. 2); the lower part with the folds would then develop into the large 

 folds surrounding the mouth in the grown animal. This question I am not able to solve definitely, 

 having only insufficient material of the following stages, in which this development must take place '). 



The infundibulum (PI. VII, Figs. 3, 10, PI. VIII, Figs. 12 — 13) is quite short, with thin, non-cili- 

 ated, walls; from each side of it, in the sagittal plane, proceeds upwards a narrow canal, which opens to 

 the exterior — the excretory canal. 



The general appearance of the gastro vascular system is easily .seen on removing the 

 epidermis of the embryo. (PI. Ill, Figs, i, 4, 6). Under each pair of costae protrudes a large sac (e. s.) 

 there being four such sacs in all. At their base they are united two and two below each tentacle 

 apparatus; the cavity of the sacs is in direct connection with the infundibulum through the main cavity 

 formed by their uniting in the middle line (PI. VIII, Figs. 12 — 13).— It is easily seen that these four large 

 sacs correspond with the four entodermal sacs of other Ctenophoran embryos. (Comp. Cliun. Mono- 

 graph, p. 115 — 116, Taf. VIII). In the sections the walls of the entodermal sacs are seen to consist 

 partly of very large, vacuolated cells, i^artl)- of a quite low epithelium. In the outer part of the sacs 

 the large cells are distinctly arranged in two separate groups (comp. PI. IX, Fig. 13, PI. X, Figs. 2 — 5), 

 the structure being thus already the same as that of the gastrovascular canals of the grown animal. 

 (Also in other Ctenophores the differentiation of the cells of the entodermal sacs begins at the corre- 

 sponding stage of development. Chun. loc. cit.). The tentacular vessels have not acquired their def- 

 inite shape as yet; the large entodermal cells are seen to fill out the two sides of the tentacle base 

 (PI. X, Figs. 3 — 5), but there is no lumen discernible as yet. 



The genital organs have not }et been formed, and I have been unable to find in the 

 sections any grouping of young cells which might be interpreted as representing the first rudiments 

 of them. 



The musculature has already reached a considerable development, as seen by the sections 

 (PI. VIII — X; comp. also PI. VII, Figs. 3, 10). It is especially well developed in the lobes. 



On reaching this stage of development the embryo is ready to leave the brood chamber. 

 Having ruptured the egg-membrane, and probably at the same time the covering epidermis of the 



') The .structure of the jiharyux of ilcrtcnsia omtni, as described ill the second part of this memoir, does uot leave an}- 

 doubt as to how these structures in Tjalficlla must be interpreted. In J/, ovum there is a narrow upper part without folds, 

 compressed in the sagittal plane; below this part the pharynx widens considerably, the strongly developed pharyngeal (or 

 stomodaeal) folds ("Magenwiilste") occupying the lateral (transversal) walls. The upper narrow part, which may be distinguished 

 as the oesophagus, evidently corresponds to the narrow canal leading from the "suboral" cavity to the infundibulum in 

 Tjatfulla, designated above (p. 8) as the pharynx (I>1. IV, Fig. 4; PI. VII, Fig. 2); this part should then likewise be designated 

 as the oesophagus (as it is, in fact, designated in the figures). The lover part, the pharynx s. str., corresponds to the 

 whole of the "suboral" cavity of Tjalfiella, the large folds, situated laterally (transversely) to the "mouth", being 

 beyond doubt homologous to the pharyngeal folds of Mertensia and the other Ctenophores. It follows 

 further that what has above ip. 8, PI. Ill, Fig. 11. o) been designated as the true mouth-opening, is really only the opening 

 from the pharynx into the oesophagus. To the mouth-opening in typical Ctenophores corresponds in Tjalfiella the opening in 

 the basal surface + the two "chimney"-opeuings. — It was only after the above had been printed that the,se facts became 

 clear to me on examining some specimens of Mertensia ovum. 



